Operational efficiency and overall output of a gas turbine engine generally increases as the temperature of the hot combustion gas stream increases. High combustion gas stream temperatures, however, may produce high levels of nitrogen oxides and other types of regulated emissions. A balancing act thus exists between operating a gas turbine engine in an efficient temperature range while also ensuring that the output of nitrogen oxides and other types of regulated emissions remain below mandated levels.
Lower emission levels of nitrogen oxides and the like may be promoted by providing for good mixing of the fuel stream and the air stream before combustion. Such premixing tends to reduce combustion temperatures and the output of nitrogen oxides. One method of providing such good mixing is through the use of micro-mixers where the fuel and air are mixed in a number of micro-mixing tubes within a plenum before combustion.
During operation, however, temperature differences may arise between the various components of a micro-mixing nozzle. For example, the interior components of the nozzle may be at about the compressor discharge temperature while exterior components, such as an aft plate, may reach the higher temperatures of the combustion products. This temperature differential may cause the aft plate to expand relative to the nozzle. Given that the aft plate may be fixedly attached to the nozzle, such growth may result in excessive strain. Such strain may significantly affect the life of the aft plate and nozzle as a whole.
There is thus a desire for an improved micro-mixer nozzle design. Such an improved micro-mixer nozzle design may promote good fuel-air mixing while accommodating temperature differentials across the aft plate and other components therein.